I agree with Aqua Sleight and rainy. I personally subscribe to the view that love is like energy, it never really dies, it sort of just diminishes in intensity or changes to another emotion. That's why they say love sometimes changes to hate.
DH had a great love before me and he has kept a picture of her tucked away in his papers. I don't mind. I had a love too, that I have no picture for, but remember fondly. I still remember what that love felt like, but context is everything. It doesn't stop me loving DH.
Most people will have several loves over a life time. Even painful loves. With time and distance, It's healthier to acknowledge their impact on your life and place them in context, than try and pretend they never existed, or waste time hating them.
I don't think you have anything to be worried about.
The other thing to consider is she's not just an ex, she an ex he shares a child with and from personal experience, having a child with someone, it adds a something, I don't know what to call it, a sort of tie that never dies, even if you hate the person you had kids with that 'something' remains. So I think you have to be a little bit more realistic about the level of importance his ex had in his life and emotions that may be very much inert but may haunt occassionally. But none of those emotions are strong enough to threaten what you have built together now.